An issue with this contrived example, as well, is that Rx has an error flow at the stream level, so typically you are more likely to build things similar to:

   userActions(combined)
    \
     \--u1-----------------e1--X
      \--u2---------------------------e2--X
       \--u3--...
        \--u4--...
         \--u5--...
          \...
           e1
            \
             X

While you could do your analytics message on the combined diagonal stream, you'd probably want to do it on the horizontal streams.